1. Field of the Invention
The invention relates in general to asphalt composition shingles and in particular to a means and method for recycling waste asphalt shingles back for re-use as a raw material for the shingle production process by grinding shredded shingles in combination with limestone ore.
2. Description of the Related Art
For some time now, asphalt roofing manufacturers have been struggling with the problem of disposal of waste asphalt shingles product. With landfill regulations becoming more stringent, recycling defective/blemished new shingles and even local "tear-off" (used) shingles back into the production process would have the distinct advantages of eliminating escalating disposal cost and reducing the requirement for fresh raw materials.
U.S. Pat. No. 4,706,893 issued to James Brock discloses a method and apparatus for recycling roofing shingles as an additive to asphalt paving composition for roadway use. The shingles are comminuted to a particle size which are then added to liquid asphalt and thoroughly mixed to produce an asphalt paving composition. U.S. Pat. No. 5,201,472 issued again to James Brock discloses a method of preparing and storing recyclable roofing shingles for asphalt paving composition. The patentee discloses that the comminuted shingle particles of his earlier patent tended to stick together. He solves this problem by mixing the asphalt roofing shingles with a carrier aggregate to prevent the shredded asphalt roofing pieces from sticking together.
Currently, there is no known process whereby waste asphalt composition shingles have been successfully recycled as a raw material for new shingle production. New shingle production requires a smooth application and absorption of a homogeneous asphalt material to a fiberglass mat as opposed to a batch mixing of bulk ingredient materials such as Brock employs in his production of paving asphalt. Some of the methods that have been contemplated and/or attempted include the following:
1. a method of using highly reactive cutting solvents to dissolve and extract the asphalt from the waste shingle. The solvents would then be extracted from the asphalt by evaporation or distillation. The problems inherent in this process are that the solvents pose very dangerous health and environmental conditions. PA1 2. a method of running the shingles through a series of high pressure rolls, similar to calender rolls in a paper mill, thereby causing compression to the shingle. Theoretically, there would be heat generated during compression and the shingles would be crushed into a pasty mass which then could be scraped from the rolls with doctor blades and then somehow be added back to the manufacturing process. PA1 3. a method of grinding the shingle while submerged under a suitable liquid. The resulting product would be a granule sized aggregate that would be used as head-lap granules on the surface of the shingle (head-lap is the term given to the unexposed surface of the shingle).
None of the above processes ever obtained practical application. U.S. Pat. No. 5,385,426 discloses milling roofing shingle pieces to particles and granules and impinging the particles and granules with intermittent blasts of compressed air and pressurized water to prevent clogging and sticking inside a hammer mill and to assist in discharging the reduced shingle material. This patent again shows the inherent sticking problems associated with this art and the lengths those skilled in the art will undertake to solve or just cope with the problem. Physical characteristics of asphalt present very difficult obstacles when attempting to separate its composition constituents and/or reduce its size through dissolving, milling, crushing or grinding. Asphalt has a relatively low softening point of approximately 200.degree. Fahrenheit. At higher temperatures it becomes viscous to the point of liquid, and at lower temperatures it becomes gummy to solid. Consequently, there is a tendency for asphalt shingles to gum up and stick to equipment that is employed for reprocessing tasks, such as those enumerated above. Additionally, the product resulting from such processes tends to become one agglomerated mass which cannot be easily handled. Accordingly, it would be desirable to have a means and method by which asphalt composition shingles could be ground to a very fine particulate suitable for an admix to the raw materials used for asphalt shingle production. Further, it would be even more desirable if that asphalt particulate did not agglomerate in the grinding process, but rather formed an easily handled powder that could be stored and uniformly controlled when recycled back to the manufacturing process.